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Print a given matrix in reverse spiral form

Given a 2D array, print it in reverse spiral form. We have already discussed Print a given matrix in spiral form. This article discusses how to do the reverse printing. See the following examples.

Input:
        1    2   3   4
        5    6   7   8
        9   10  11  12
        13  14  15  16
Output: 
10 11 7 6 5 9 13 14 15 16 12 8 4 3 2 1
Input:
        1   2   3   4  5   6
        7   8   9  10  11  12
        13  14  15 16  17  18
Output: 
11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1



C++

// This is a modified code of
#include <iostream>
#define R 3
#define C 6
using namespace std;
  
// Function that print matrix in reverse spiral form.
void ReversespiralPrint(int m, int n, int a[R][C])
{
    // Large array to initialize it
    // with elements of matrix
    long int b[100];
      
    /* k - starting row index
    l - starting column index*/
    int i, k = 0, l = 0;
      
    // Counter for single dimension array
    //in which elements will be stored
    int z = 0;
      
    // Total elements in matrix
    int size = m*n;
  
    while (k < m && l < n)
    {
        // Variable to store value of matrix.
        int val;
          
        /* Print the first row from the remaining rows */
        for (i = l; i < n; ++i)
        {
            // printf("%d ", a[k][i]);
            val = a[k][i];
            b[z] = val;
            ++z;
        }
        k++;
  
        /* Print the last column from the remaining columns */
        for (i = k; i < m; ++i)
        {
            // printf("%d ", a[i][n-1]);
            val = a[i][n-1];
            b[z] = val;
            ++z;
        }
        n--;
  
        /* Print the last row from the remaining rows */
        if ( k < m)
        {
            for (i = n-1; i >= l; --i)
            {
                // printf("%d ", a[m-1][i]);
                val = a[m-1][i];
                b[z] = val;
                ++z;
            }
            m--;
        }
  
        /* Print the first column from the remaining columns */
        if (l < n)
        {
            for (i = m-1; i >= k; --i)
            {
                // printf("%d ", a[i][l]);
                val = a[i][l];
                b[z] = val;
                ++z;
            }
            l++;
        }
    }
    for (int i=size-1 ; i>=0 ; --i)
    {
        cout<<b[i]<<" ";
    }
}
  
/* Driver program to test above functions */
int main()
{
    int a[R][C] = { {1, 2, 3, 4, 5, 6},
                    {7, 8, 9, 10, 11, 12},
                    {13, 14, 15, 16, 17, 18}};
    ReversespiralPrint(R, C, a);
    return 0;
}

Java

// JAVA Code for Print a given matrix in 
// reverse spiral form
class GFG {
  
    public static int R = 3, C = 6;
      
    // Function that print matrix in reverse spiral form.
    public static void ReversespiralPrint(int m, int n,
                                             int a[][])
    {
        // Large array to initialize it
        // with elements of matrix
        long b[] = new long[100];
           
        /* k - starting row index
        l - starting column index*/
        int i, k = 0, l = 0;
           
        // Counter for single dimension array
        //in which elements will be stored
        int z = 0;
           
        // Total elements in matrix
        int size = m * n;
       
        while (k < m && l < n)
        {
            // Variable to store value of matrix.
            int val;
               
            /* Print the first row from the remaining 
            rows */
            for (i = l; i < n; ++i)
            {
                  
                val = a[k][i];
                b[z] = val;
                ++z;
            }
            k++;
       
            /* Print the last column from the remaining
            columns */
            for (i = k; i < m; ++i)
            {
                  
                val = a[i][n-1];
                b[z] = val;
                ++z;
            }
            n--;
       
            /* Print the last row from the remaining 
            rows */
            if ( k < m)
            {
                for (i = n-1; i >= l; --i)
                {
                      
                    val = a[m-1][i];
                    b[z] = val;
                    ++z;
                }
                m--;
            }
       
            /* Print the first column from the remaining 
            columns */
            if (l < n)
            {
                for (i = m-1; i >= k; --i)
                {
                      
                    val = a[i][l];
                    b[z] = val;
                    ++z;
                }
                l++;
            }
        }
          
        for (int x = size-1 ; x>=0 ; --x)
        {
            System.out.print(b[x]+" ");
        }
    }    
      
    /* Driver program to test above function */
    public static void main(String[] args) 
    {
        int a[][] = { {1, 2, 3, 4, 5, 6},
                    {7, 8, 9, 10, 11, 12},
                    {13, 14, 15, 16, 17, 18}};
          
        ReversespiralPrint(R, C, a);
         
    }
  }
// This code is contributed by Arnav Kr. Mandal.

Python3

# Python3 Code to Print a given
# matrix in reverse spiral form

# This is a modified code of
# https:#www.geeksforgeeks.org/print-a-given-matrix-in-spiral-form/
R, C = 3, 6

def ReversespiralPrint(m, n, a):

# Large array to initialize it
# with elements of matrix
b = [0 for i in range(100)]

#/* k – starting row index
#l – starting column index*/
i, k, l = 0, 0, 0

# Counter for single dimension array
# in which elements will be stored
z = 0

# Total elements in matrix
size = m * n

while (k < m and l < n): # Variable to store value of matrix. val = 0 # Print the first row # from the remaining rows for i in range(l, n): # printf("%d ", a[k][i]) val = a[k][i] b[z] = val z += 1 k += 1 # Print the last column # from the remaining columns for i in range(k, m): # printf("%d ", a[i][n-1]) val = a[i][n - 1] b[z] = val z += 1 n -= 1 # Print the last row # from the remaining rows if (k < m): for i in range(n - 1, l - 1, -1): # printf("%d ", a[m-1][i]) val = a[m - 1][i] b[z] = val z += 1 m -= 1 # Print the first column # from the remaining columns if (l < n): for i in range(m - 1, k - 1, -1): # printf("%d ", a[i][l]) val = a[i][l] b[z] = val z += 1 l += 1 for i in range(size - 1, -1, -1): print(b[i], end = " ") # Driver Code a = [[1, 2, 3, 4, 5, 6], [7, 8, 9, 10, 11, 12], [13, 14, 15, 16, 17, 18]] ReversespiralPrint(R, C, a) # This code is contributed by mohit kumar [tabby title="C#"]

// C# Code for Print a given matrix in 
// reverse spiral form
using System;
class GFG {
  
    public static int R = 3, C = 6;
      
    // Function that print matrix in reverse spiral form.
    public static void ReversespiralPrint(int m, int n,
                                            int [,]a)
    {
        // Large array to initialize it
        // with elements of matrix
        long []b = new long[100];
          
        /* k - starting row index
        l - starting column index*/
        int i, k = 0, l = 0;
          
        // Counter for single dimension array
        //in which elements will be stored
        int z = 0;
          
        // Total elements in matrix
        int size = m * n;
      
        while (k < m && l < n)
        {
            // Variable to store value of matrix.
            int val;
              
            /* Print the first row from the remaining 
            rows */
            for (i = l; i < n; ++i)
            {
                  
                val = a[k,i];
                b[z] = val;
                ++z;
            }
            k++;
      
            /* Print the last column from the remaining
            columns */
            for (i = k; i < m; ++i)
            {
                  
                val = a[i,n-1];
                b[z] = val;
                ++z;
            }
            n--;
      
            /* Print the last row from the remaining 
            rows */
            if ( k < m)
            {
                for (i = n-1; i >= l; --i)
                {
                      
                    val = a[m-1,i];
                    b[z] = val;
                    ++z;
                }
                m--;
            }
      
            /* Print the first column from the remaining 
            columns */
            if (l < n)
            {
                for (i = m-1; i >= k; --i)
                {
                      
                    val = a[i,l];
                    b[z] = val;
                    ++z;
                }
                l++;
            }
        }
          
        for (int x = size-1 ; x>=0 ; --x)
        {
        Console.Write(b[x]+" ");
        }
    
      
    /* Driver program to test above function */
    public static void Main() 
    {
        int [ ,]a = { {1, 2, 3, 4, 5, 6},
                    {7, 8, 9, 10, 11, 12},
                    {13, 14, 15, 16, 17, 18}};
          
        ReversespiralPrint(R, C, a);
          
    }
}
// This code is contributed by vt_m.

PHP

<?php
// PHP Code for Print a given  
// matrix in reverse spiral form
$R=3;
$C=6;
  
// Function that print matrix 
// in reverse spiral form.
function ReversespiralPrint($m, $n, array $a)
{
      
    // Large array to initialize it
    // with elements of matrix
    $b;
      
    // k - starting row index
    // l - starting column index
    $k = 0;
    $l = 0;
      
    // Counter for single dimension array
    // in which elements will be stored
    $z = 0;
      
    // Total elements in matrix
    $size = $m*$n;
  
    while ($k < $m && $l < $n)
    {
          
        // Variable to store
        // value of matrix.
        $val;
          
        // Print the first row from 
        // the remaining rows
        for ($i = $l; $i < $n; ++$i)
        {
            $val = $a[$k][$i];
            $b[$z] = $val;
            ++$z;
        }
        $k++;
  
        // Print the last column from
        // the remaining columns 
        for ($i = $k; $i < $m; ++$i)
        {
              
            // printf("%d ", a[i][n-1]);
            $val = $a[$i][$n-1];
            $b[$z] = $val;
            ++$z;
        }
        $n--;
  
        // Print the last row from 
        // the remaining rows
        if ( $k < $m)
        {
            for ($i = $n-1; $i >= $l; --$i)
            {
                  
                // printf("%d ", a[m-1][i]);
                $val = $a[$m-1][$i];
                $b[$z] = $val;
                ++$z;
            }
            $m--;
        }
  
        // Print the first column 
        // from the remaining columns 
        if ($l < $n)
        {
            for ($i = $m - 1; $i >= $k; --$i)
            {
                $val = $a[$i][$l];
                $b[$z] = $val;
                ++$z;
            }
            $l++;
        }
    }
    for ($i = $size - 1; $i >= 0; --$i)
    {
        echo $b[$i]." ";
    }
}
  
    // Driver Code
    $a= array(array(1, 2, 3, 4, 5, 6),
              array(7, 8, 9, 10, 11, 12),
              array(13, 14, 15, 16, 17, 18));
    ReversespiralPrint($R, $C, $a);
  
// This Code is contributed by mits 
?>

Output:

11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1

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This article is attributed to GeeksforGeeks.org

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